1. Field of the Invention
The present invention relates to an exhaust system of a multi-cylinder engine provided to automobiles and the like.
2. Description of the Background Art
Conventionally, exhaust systems aiming to increase the engine output of engines of automobiles and the like have been developed.
For example, Japanese Published Unexamined Application No. 2009-97335 (Patent Document 1) discloses a system including a turbocharger, comprising plurality of independent passages mutually and independently connected to an exhaust port of each of the cylinders, a collection part provided upstream of the turbocharger where the independent passages are assembled, and a valve provided to the collection part and which is capable of changing the flow passage area of the respective independent passages. With this system, the exhaust of the cylinder performing the exhaust stroke is caused to flow from a predetermined independent passage into the collection part at a relatively high velocity by narrowing the flow passage area of the independent exhaust passage with the valve, causes the negative pressure generated around the high velocity exhaust to work on the other independent passages in the collection part, and pumps out the exhaust in the other independent passages to the downstream side based on the so-called ejector effect. The amount of gas that is supplied to the turbocharger is thereby increased.
Demands for increasing the engine output of engines in automobiles and the like are still high, and, in particular, there are demands for increasing the engine output with a simple configuration in an engine system without a turbocharger in which its structure has been simplified.